The 5-hydroxytryptamine 2C receptor (5-HT2CR) is involved in a diversity of physiological functions, such as nociception, motor behavior, endocrine secretion, thermoregulation, appetite modulation, and the control of exchanges between the central nervous system and the cerebrospinal fluid (Iwamoto et al., RNA Biol., 6, 248-53, 2009; Bubar et al., Prog. Brain Res. 172, 319-346, 2008; Berg et al., Neuropharmacology 55, 969-76, 2008; Di Giovanni, Curr. Top. Med. Chem. 6, 1909-25, 2006; Di Giovanni, Curr. Med. Chem. 13, 3069-81, 2006; Fone et al., Br. J. Pharmacol. 123, 8, 1998). This receptor has also been implicated in numerous pathologies, and the modulation of 5-HT2CR function holds a tremendous amount of therapeutic promise for the treatment of diseases such as addiction, anxiety, depression, obesity/eating disorders, Parkinson's disease, and schizophrenia (Leggio et al., Neuropharmacology 56, 507-13, 2009; Nic Dhonnchadha et al., Behav. Brain Res. 195, 39-53, 2008; Bubar et al., Prog. Brain Res. 172, 319-346, 2008; Maillet, et al., Prog. Brain Res. 172, 407-20, 2008; McCreary et al., Neuropsychopharmacology 20, 6, 1999; Miller, Mol. Interv. 5, 5, 2005; Di Giovanni, Curr. Top. Med. Chem. 6, 1909-25, 2006; Di Giovanni, Curr. Med. Chem. 13, 3069-81, 2006). Successful development of 5-HT2CR ligands requires selectivity over the highly homologous 5-HT2AR and 5-HT2BR because activity at these receptors can result in significant adverse CNS and cardiovascular events.
Traditional screening for ligands has been optimized to detect standard orthosteric agonists and antagonists. Conversely, with increasing emphasis on cellular functional screens, more allosteric ligands are being discovered as potential medications. Allosteric modulators of the 5-HT2CR present a novel drug design strategy to augment the response to endogenous 5-HT in a site- and event-specific manner (Conn et al., Nature Reviews Drug Discovery 8, 41-54, 2009). In addition, there are theoretical reasons that allosteric ligands may be preferred therapeutic chemical targets including the prospects for increased selectivity, better control of physiological systems, as well as separate control of affinity and efficacy (Kenakin, J. Biomol. Screen. 15 (2), 119-130, 2010). To date, PNU-69176E, identified via a chemical library screen, is the only synthetic compound that has been reported as a selective allosteric modulator of 5-HT2CR (Im et al., Mol. Pharmacol. 64, 78-84, 2003; Ding et al., ACS Chem. Neurosci. 3, 538-545, 2012); however, the relevant structure-activity relationship (SAR) studies are sparse, and thus knowledge in this regard is quite limited.
Thus, there remains a need for additional specific allosteric modulators of 5-HT2CR.